This invention relates generally to micro-machined three dimensional structures, and in particular to micro-machined movable structures.
Conventional bar code scanners are used to scan a surface with a laser beam. Conventional bar code scanners further typically utilize mirrors that are oscillated to permit the laser beam to scan. Conventional mirrors for bar code scanners are relatively large and imprecise.
In order to manufacture smaller and more precise bar code mirrors, micromachining processes are commonly used in which a silicon substrate is micromachined to produce a mirror. However, conventional micromachining processes suffer from a number of limitations.
For example, in micromachining an initially planar substrate using repeated iterations of photolithographic patterning and etching, it is typically desirable to etch the substrate to achieve etch depth variations that are greater than those appropriate for conventional photolithographic patterning methods used in manufacturing integrated circuits. In some cases, the etch depth variation of the substrate may exceed the depth of focus of the optical lithography equipment. The variation in etch depth may also be sufficiently large to preclude the application of a thin, uniform layer of photoresist using the conventional technique of pouring photoresist onto the substrate and then rapidly spinning the substrate to distribute the photoresist. If photoresist is spun onto a surface having significant topography, then the resulting thickness of the photoresist may vary by more than 1000%. As a result, lithography of fine features in uneven photoresist is difficult because of the overexposure of the thinner photoresist regions. However, in typical micromachining applications, it is typically desirable to subsequently pattern such a substrate having significant topography.
An additional complication arises during micromachining if relatively deep recesses are formed on one side of a substrate and then the other side of the substrate is micromachined. Typical vacuum chucks of conventional automatic wafer handling equipment may not be able to hold such wafers due to the uneven micromachined surface.
In order to overcome some of the difficulties of micromachining, a number of so-called merged-mask micromachining processes have been developed. The typical processing steps in a merged-mask micromachining process include forming all of the etching masks onto the substrate, and then micromachining the substrate. In this manner, the etching masks are formed on a substantially planar surface resulting in relatively consistent and even film thicknesses. However, the conventional merged-mask micromachining processes still suffer from a number of limitations.
The present invention is directed to overcoming one or more of the limitations of the existing micromachining processes.